How Muscles Recover From Nerve Injuries

An Overview of How Muscles Recover from Nerve Injuries

Muscles have different ways to recover or adapt to nerve injuries. There are four types of nerve injuries that can occur. This section will discuss those injuries and how muscles recover from nerve injuries.

Nerve Injury Types

Functional Compression Nerve Block

The first nerve injury is called a functional compressive nerve block. This type of block we have all experienced when we rest our ulnar nerve (the “funny bone”) on a hard surface. This position allows the ulnar nerve to be compressed and the nerve then stops working. This is due to a lack of the normal chemical transmission through the nerve membrane. The outside of the hand “falls asleep”. When the pressure is removed, the chemical imbalance resolves and the nerve starts transmitting almost immediately. Sensation and muscle function then returns.

Functional Myelin Injury Nerve Block

The second injury is easily recoverable in function. This conduction block is due to an injury to the myelin sheath. The myelin sheath is the insulation found on larger nerves and is required to be intact to allow the signal to pass down these nerves. An injury to the myelin sheath with the nerve itself remaining intact will cause the conduction to be blocked but nerve cell itself remains normal. The injured myelin sheath will repair itself and the nerve will conduct normally again. Repair of this sheath requires between four to twelve weeks to fully recover.

Wallerian Degeneration (Loss of the Nerve Axon with an Intact Myelin Sheath)

In this type of motor nerve injury, the long body of the nerve (the axon) is injured but the myelin sheath (the insulation) remains intact. This will produce a situation called Wallerian Degeneration. In this setting, the nerve will regrow down its old pathway through this intact myelin sheath tunnel and reconnect to the muscle once again. This implies that the pathway for the nerve (the myelin sheath) is not damaged.

The motor nerve will grow down an intact myelin sheath at about one inch per month. As an example, an injury to the S1 nerve at the spinal level L5-S1 where a disc herniation typically occurs to injure the nerve means that this nerve needs to grow down the sheath more than two feet. That translates to 24 months at one inch a month.

The problem with this delay in reattachment is that the muscle without a nerve supply will become fibrotic (meaning useless) in a period of 12-18 months. Muscles that are eighteen inches or less from the nerve injury (assuming an intact myelin sheath) will still have a chance to function. Muscles in the thigh and the entire arm generally fit this description when the nerve is injured by spine compression (herniated disc or bone spur).

Unfortunately, the muscles in the lower leg and foot are generally too far from the injury to recover from a spinal issue in the lower back. This includes L5 and S1 nerves and some of the muscles supplied by the L4 nerves. There are some L5 and S1 innervated muscles (buttocks and thigh) that are close enough to recover in this type of nerve injury.

Nerve and Myelin Cell Death

The fourth type of motor nerve injury is found with more prolonged or severe compression that actually causes the nerve cell itself to die along with the myelin sheath. This nerve cannot regenerate and the muscle cell will remain without a nerve connection.

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Nerve Budding/Sprouting

If any muscle cell has no nerve input for a period of time, the muscle generates a chemical signal for help. Any intact motor nerve in the immediate area will sprout and will send a new branch to this muscle cell. This budding process takes between ten to sixteen weeks. When the muscle cell is reconnected, this muscle cell can contract.

On the EMG, this appears as a more coarse contraction. Intact axons (nerve cells) can bud up to ten times. That is, a single nerve can pick up ten times the number of muscle cells it normally services.

If the nerve is so severely damaged, there may not be enough intact functioning nerve cells immediately around the surrounding muscle. These muscle cells will fibrose (die).

Nerve budding or sprouting also occurs in the situation where the nerve can still regenerate (see Wallerian Degeneration) but regeneration takes a longer period of time than the process of budding will take.

Compensatory Hypertrophy

Another recovery function has to do not with muscle re-innervation but with muscle conditioning. The remaining muscle cells that continue to function can hypertrophy to compensate for the missing cells. I call this “Arnold Schwarzenegger compensation”. This is where physical therapy can help to condition and strengthen the remaining functioning muscle cells to compensate for the missing muscle cells.

Treatment of Nerve Injuries

The problem for the spinal clinician is that there is no way to know which injury has occurred to the nerve in the case of a nerve compression syndrome (herniated disc or spur). In the presence of nerve compression with weakness due to herniated disc or bone spur, it is my opinion that the nerve needs to be surgically decompressed as time of compression most likely makes a difference in recovery.

Once the nerve is decompressed, the only way to really know about the type of injury is with “tincture of time”. Recovery will occur based upon the timelines noted above. That is, functional compression injuries will immediately recover, myelin sheath injuries will take between four to twelve weeks to recover, nerve budding will take ten to sixteen weeks and full nerve injuries with the myelin sheath intact will take as long as the length of the nerve to the muscle (up to one year). If weakness has not recovered in one year, the nerve will generally not recover and the weakness will remain.

Therapy should be instituted for work on strengthening and to compensate for any weakness that might lead to further injury (ankle weakness can lead to ankle sprain/fracture or knee weakness that could lead to a fall). Braces or walking aids such as a cane or walker might be necessary to help with function and prevent injury.

To learn more about how muscles recover from nerve injuries, or to discuss your nerve injury with a spine surgeon and back specialist, please contact the office of Dr. Donald Corenman located in the Vail, Aspen, Denver and Grand Junction, Colorado area.

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81 reviews

Eric S

Sep 26, 2021

by Eric S on Donald Corenman, MD, DC

Successful pars repair at 46 years old

Back in November of 2018 (at 46 years old) I came from Vancouver BC to have a pars repair done with Dr. Donald Corenman at the Steadman Clinic in Vail Colorado. I'm finally posting this review nearly three years later in late 2021. The reason I waited so long was I wanted to know the final result before I posted my review. Unfortunately in that time Dr. Corenman has retired. Nevertheless, I want to post this review of Dr. Corenman and his staff at the Steadman Clinic in their excellent treatment of my L5 pars interarticularis.

I fractured my pars at age 42 back in 2014 when rolling on the gym floor, and was denied treatment by the Canadian healthcare system, probably due to my age. First my GP told me there was no surgical option for a pars defect, which was quite incorrect! I tried to live with it, but the symptoms worsened (periodic random spine slippage and weeks of resultant pain after just bending over to tie my shoe, so I eventually learned to mostly squat and hardly bend). When I finally consulted with Canadian spine surgeons, I was told they believed my pars defect had been congenital (since birth). This was absurd, considering I had done extreme martial arts (including jiu jitsu) for years prior, as well as 5 years of reinforcing steel full time in my 20s, probably the hardest job on the back you can find. No pars defect like mine would possibly have allowed this--ergo it was impossible that I had had the defect since birth. I did however have an asymptomatic congenital spina bifida occulta that made me more susceptible to a pars fracture. In 2014 in one instant, I went from having the strongest back people I knew said they'd ever seen, to being unable to safely bend over and tie my shoe without a non-negligible risk of my spine slipping randomly (which would lead to weeks of pain after each occurrence). This was due to the unilateral L5 pars defect, otherwise known as spondylolysis. It was when lying in pain on the floor 4 years later after maybe the 6th spine slippage event post injury, that I had had enough, and resolved to have surgery. If Canada's "universal health care" said no, I would make lemonade from lemons, and find the very best surgeon in the world at pars repairs. That was Dr. Donald Corenman. Dr. Corenman back in 2018 ran a website https://neckandback.com/ that dedicated many pages to the science of every aspect of pars repairs, from eligibility (good discs on MRI), to best surgical techniques (minimal open compared to minimally invasive), best imaging to use (i.e., O-Arm with Stealth imaging vs. older fluoroscopy), the ideal amount of BMP to use and why not use too much or too little, and much more, all to do with pars repairs, pages upon pages of his site just on the pars, with scientific references and his own extensive expert opinion. As a health research statistician, I was very impressed with this. It was in stark contrast to the websites of other spine surgeons which barely gave the pars a word or two, focusing almost exclusively on fusions. I had found the best surgeon in the world for pars repairs, and so after Dr. Corenman personally screened my MRI to ensure my discs were healthy, I booked the surgery.

Being 46 years old at the time of surgery in 2018, with a 4-year-old pars fracture from 2014 combined with a congenital SBO meant my pars fragment was somewhat atrophied, but it was "very solid", said Dr. Corenman in the operative report. Nevertheless, it was challenging with two things to fix, the pars and SBO, and OR time was around 4 hours. Recovery over the following months was guided by a very clear "Spine binder" from the Steadman Clinic with strict rules of "no BLT" (no bending, lifting or twisting), and illustrated physiotherapy guidelines. They even warned patients to avoid fish oil supplements, which could excessively dampen inflammation and hence slow bone healing. They answered many questions I had during months of recovery, with responses coming from the very supportive Lori Fugate (then director of Dr. Corenman's practice), and Ehrich Bean (then physician's assistant at the practice), as well as a couple calls with Dr. Corenman himself after two of the CT scans. Ehrich Bean offered great advice for taking the spine binder conservatively due to the nature of pars repairs vs. fusions. The final post-op CT scan I had was a couple weeks ago at 34 months post-op, and Dr. Corenman had retired, but I got a very positive and informative call from Eric Strauch (current PA at the Steadman Clinic under Dr. Corenman's replacement there, and who had also worked with Dr. Corenman previously). The staff at the Steadman Clinic were extremely supportive all the way through the process. I should mention, the local Canadian spine surgeon did offer me very good post-operative support including antibiotics as needed to deal with a mild surface incision-site infection early on, booking numerous x-rays when I felt something was amiss, as well as booking all four of my post-op CT scans. I am very grateful for that support also.

My final result shows plenty of solid bone across the pars and a healed SBO, with my vertebral body now a solid bone ring instead of being broken at two places as it was pre-op. Does my spine hold up in the real world? You bet! I have recently dug and moved several yards of dirt and sand and gravel by myself (shovel and wheelbarrow!) to fix our water main, pulled roots from the yard, moved several "portable" (these are HUGE) air conditioners up several flights of stairs my myself, and lifted weights. I now run 2 miles (3.2 KM) several times weekly with a hard 100 meter dash in the middle. I bend deeply before each run I go on, with no spine slippage. My spine feels amazing. I can bend over to do exercise, or real word tasks, with no risk of spine slippage.

My sincere thanks to God, Dr. Donald Corenman, Lori Fugate, Ehrich Bean, Eric Strauch, and the Steadman Clinic, as well as the Canadian spine surgeon who offered me excellent post-operative care back in Canada. You have all given me a new lease on life.

Sincerely,
Eric S

Robert S

May 11, 2021

by Robert S on Donald Corenman, MD, DC

Back Fusion Surgery

I had my entire lumbar spine fused in November of 2018. I had scoliosis , with pinched nerves that were so painful I could hardly walk - and standing for more than a few minutes was impossible. Even sitting was painful.
The fusion surgery produced immediate relief! And the recovery was much easier than I expected.
To this day I can do all the activities I love from hiking, to standing in a stream fly fishing to riding my bike long distances - or just walking down the street with my wife.
Kudos to Dr. Corenman and his staff, (including the two Erics) for taking such good care of me!

Leslie R

Jul 9, 2020

by Leslie R on Donald Corenman, MD, DC

TLIF

I had my TLIF surgery on 6/24/2020 by Dr. Corenman, I can not say enough good things about the Dr or his staff. I was always treated with respect and explained everything throughly, that made it easy for everyone to understand. I highly recommend Dr. Corenman and the Steadman Clinic.

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How Muscles Recover from Nerve Injuries